This invention relates to a method and apparatus for dilating blood vessels in vasospasm.
Vasospasm is an abnormal and often persistent contraction of an artery that reduces the caliber of the artery and may critically reduce blood flow. Vasospasm can produce a partial or complete obstruction in arteries that otherwise appear completely normal. Greater or lesser amounts of dynamic or spastic constriction at the point of a fixed obstruction can create a severe reduction of flow even where the fixed obstruction itself would be clinically benign.
Vasospasm can occur spontaneously; or it may occur as the result of certain pharmacological stimuli, such as, for example, ergonovine testing; or of mechanical stimuli such as contact with a surgical instrument or a diagnostic or therapeutic catheter, for example as a complication of percutaneous transluminal catheter angioplasty (PTCA); or of environmental stimuli. Raynaud's phenomenon and Printzmetal angina are two additional forms of vasospasm. Furthermore, certain maladies such as subarachnoid hemorrhage can also lead to vasospasm. In particular, cerebral vasospasm, which is caused by subarachnoid hemorrhage, and opthalmic artery vasospasm may cause severe consequences if not treated promptly.
Various medications have been tested for the relief of vasospasms and are only partially effective. For example, vasospasm in coronary vasculature has been treated with calcium channel blockers. However, for some unknown reason that relates to the pharmacological and anatomical differences between cerebral and coronary vasculature, these drugs are ineffective against cerebral vasospasm. In addition, mechanical treatment such as balloon angioplasty is also ineffective against cerebral vasospasm.
Other non-chemical treatments, e.g., laser irradiation-induced dilation of the vessels, of vasospasm have likewise been relatively unsuccessful or plagued with various problems. For example, laser irradiation-induced dilation of blood vessels is cumbersome, may damage surrounding healthy tissue, does not use standard catheter guide wire techniques, and provides a narrow margin between the laser energy needed to cause vasodilation and that needed to perforate the vessel wall. Moreover, in those laser techniques using low level constant wave laser radiation, vasospasm resumes as soon as the radiation ceases.
Furthermore, mechanical dilation treatments, such as balloon angioplasty, are generally ineffective because, vasospasm generally resumes after the balloon is removed, and these treatments are very difficult in arteries that are hard to catheterize, e.g., the ophthalmic artery.